How Deforestation Gives Rise To Human Disease?

March 11, 2017 by NILAKSHI PATHAK

By and large, we are taught that deforestation leads to environmental degradation and other environmental problems. In fact, the problems created by deforestation are atrocious for all organisms. We all know about its impact on the environment. Having said that, what about its impact on the human? I would like to draw your attention to the link that exists between deforestation and human disease. I would like to start with a case study so that a better understanding is developed in analyzing the correlation.

Case Study of Deforestation in Borneo Island

Borneo is the largest island of Asia and third-largest island in the world. It is shared both by Malaysia and Indonesia. It is one of the oldest rainforests in the world. But it seems like very soon, we will be replacing ‘is’ with ‘was’. The diagram below shows the pace of deforestation in Borneo Island.

The forests are cut at such a tremendous rate to meet the demands of plywood industry and palm oil plantations. The worrisome effects of this action are:

Destruction of wildlife habitat.

Release of stored carbon

Increase in the spread of disease

It has been noticed by the researchers that as the deforestation is increasing in the region, the number of human malaria cases are also increasing. The observation has been documented in ‘Journal of Emerging Infectious Diseases’.

What Was Observed In Borneo Island?

The sudden spike in human malaria cases drew the attention of many researchers. Satellites maps were studied. In the studies, it was observed that the malarial cases were reported in the region where the deforestation took place. The malaria form which is now prevalent among the people living there was once found in primates called macaques. Now the question that arises is how the disease was transmitted from macaques to human? Researchers have explained that because of the ongoing deforestation, the macaques concentration in patches of habitable forest. As a result, the disease grew among their own population. As human began to clear this forest region also, the mosquitoes that thrived in that habitat helped in transmitting the disease from the macaques to human. Other carriers of pathogens apart from mosquitoes are bats, primates and snails.

Peter Daszak, president of Ecohealth Alliance says, “In years when there is a lot of land clearance you get a spike in leptospirosis cases, and in malaria and dengue. Deforestation creates an ideal habitat for some diseases.”

The Relation Between Forests and Diseases

It is not a new piece of information that most of the pathogens that cause human diseases spend part of their life cycle in animals. Do you know what does that mean? It means chances are very high that reason for the next global pandemic will be out from the forest. Also, let me tell you SARS and Ebola, both have emerged from wild animals. What’s more the world knows how it has affected us.

The Zika virus got its name from Zika forest of Uganda. The disease causes microcephaly (abnormal small heads). It has affected most part of Latin America. Even the pathogens for Dengue, Chikungaya and Yellow Fever have emerged out of the forest.

Since a very long time, the numerous pathogens that are present in the forest are transmitted back and forth between mosquitoes and mammals. But the point here is the evolution of pathogens and the organisms residing in the forest have taken place together. And therefore, you will see from few to no symptoms in the animals affected by these pathogens. But have human evolved along with these pathogens? The answer is no and thus you can see the rising human diseases.

How Does Deforestation Create Ideal Situation For Mosquito Breeding?

Rainforests are so densely populated by canopies that it has a shady forest floor. When these forests are cleared, sunlight starts flooding in the shady region. This increases the water temperature of the area and this helps in providing an ideal situation from mosquito breeding.

Also, the leaves provide tannins to the nearby streams and ponds. But when these tannins disappear the acidity of the water is lowered and the water becomes more turbid. Again, this favours mosquito breeding. The water table also rises in the region as the water is not taken up and transpired by the trees. This gives rise to swampy areas.

The Danger Of Replacing Forest With Human Wants

When the forest is replaced by agriculture, we are replacing tall trees with low-lying vegetation. And the low-lying vegetation creates a more suitable environment for the growth of the malarial parasite. Even when forests are cleared for other human wants, we are again inviting an increase in disease. Let me provide you an example to explain it. In the 1990s, the number of malaria cases was 600. The number of cases rose to 120,000 when a road was built in the forested area.

When we do deforestation, we create new boundaries between deforested area and forest. Aedes Africanus, a mosquito, resides in this edge habitat. The mosquito is responsible for Yellow Fever and Chikungunya virus. There are many other primates who also gather in these boundary regions and provides a constant source of pathogens to the insects. These insects then bite the people who work or live in the nearby region.

It is very easy for a disease to spread, once it has left the forested area. Take for example the Zika virus which travelled from Africa to Brazil. I have mentioned earlier that even bats can act as a carrier of diseases. A good example of this is Ebola virus that killed 11,000 people last year. The Ebola virus is harbored by Angolan tailed bats.

The Main Question

The main question that the researchers are asking is “What pathogens might come out of the forest in the future?” We don’t have the answer but let me ask you, do you really want to know the answer?

Why can’t we just say no to deforestation to avoid all these problems? I would like to wrap up the article with a quote by Ed Begley Jr. Do think about it.

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